The aforementioned application is directed to a system for detecting leaks in installations such as underground gasoline storage tanks, which are connected with liquid withdrawal systems in the form of above-ground gasoline pumps at the service station. Such underground tank bodies have upwardly projecting fill and vent pipes. The previous system was designed to avoid the necessity of measuring and compensating for differences in the temperature of the liquid in the tank at various depths in order to accurately indicate the presence of a leak of a magnitude to necessitate repair or replacement of the tank.
State law in many jurisdictions requires, for example, that there be a periodic monitoring of such tanks, in a manner to achieve a leak detection of as little as 0.05 gallons per hour, and, of course, many operators, concerned with environmental considerations and eliminating potentially explosive conditions, seek even more stringent monitoring systems.
Among various systems which have been proposed previously, and which indicate the state of the art at the present time, are the following:
______________________________________ 1,598,571 Fox et al 4,006,636 Hohmen 3,580,055 White 4,186,591 Mooney 3,587,316 Kapteyn 4,300,388 Hansel et al 3,818,752 Lindeberg 517,388 Linder 1,720,159 Willmann 3,961,532 Kukuruzinski 2,012,511 Hubbard 4,108,002 Rowe et al 2,853,874 Mennesson 4,362,403 Mooney 3,726,141 Bremer et al 4,472,969 Templin ______________________________________
My prior system utilized a bubbling technique, wherein a continuous stream of bubbles of air was forced into the liquid near the bottom of the tank and the resistance to air introduction, as influenced by the composite effect of the pressure of the gas on the level of liquid in the tank and the head of liquid at the level of gas introduction, was balanced against the static pressure of the gas in the space above the liquid as a reference pressure to note any differential pressure variation over a time period.